Numerous manufacturing processes call for on-line monitoring of a physical property of a free flowing granular or particulate material. Examples of properties to be monitored are moisture content, temperature, color, etc. An example of a process where on-line monitoring is employed is manufacturing of feed. A difficulty is encountered in presenting to the on-line sensors a representative sample of the free flowing material in order that the on-line assay will be meaningful. That is, what is "seen" by the sensor must accurately represent the process stream. Physical characteristics of free flowing particulate materials compound the basic problems encountered when placing an on-line sensor in a process stream. Any attempt to divert or restrict the particulate flow invites plugging or bridging. This is particularly true of sampling devices employing a conical or pyramidal shape that abruptly restricts the particulate flow from all directions as it enters the inlet. Plugging or bridging stops flow through the sensing device. In addition, the flow pattern of the particulate material is seldom uniform. Augers, bucket elevators and such devices are commonly used to move the particulate material, giving the flow pattern a pulse. The particles comprising the stream are frequently of irregular shape and size.